Amplifier tube control



Aug. 16, 1932. w A ROBERTS 1,872,347

AMPLIFIER TUBE CONTROL Filed March 30, 1929 WALTER VAN B. ROBERTS Patented Aug. 16, 1932 UNITED STATES PATENT OF F ICE- WALTER VAN B. ROBERTS, OF PRINCETON, NEW JERSEY, ASSIGNOR TO RADIO COR PORA'I'ION OFAMEBICA, A CORPORATION OF DELAWARE V AMPLIFIER roan CONTROL My present invention relates to amplifier tubes, and, more particularly, to a transmitter amplifier circuit employing a portion of its input to control tion.

In operating a transmitter, the amplifier tubes should, for ideal performance, be sub- 7 jected to maximum plate heatingonly when the radio frequency input is at a maximum. By employing an expedient which involves the utilization of a portion of the'input radio frequency current, I achieve satisfactory performance of the amplifier tubes.

It is one of the main objects of the present invention to provide an amplifier tube operating in such a manner that the biasing potential on its grid is reduced when the input is of a large amplitude, and the grid bias is at a maximum when the input to the tube is small, thus resulting in control of the plate current consumption.

Another important object of the invention is to provide an amplifier tube in a transmitting circuit, which tube is biased highly negative when the tube is not subjected to radio frequency impulses, and additional means to supply a variable potential counter to the grid biasing potential in accordance with input variations.

Still another object of the invention is to provide an amplifier tube circuit which includes in the grid circuit of the tube means, responsive to variations in the radio frequency input, to supply a filtered continuous current to the said grid circuit, the potential of the current being counter to the biasing potential of the grid whereby the average current flowing through the plate circuit of the tube increases with the input amplitude.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claim, the invention itself, however, as to both its organization and method of operation, will best be understood by reference to the following description taken in connection with r the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into effect.

plate current consump- In the drawing, r Fig.1 is a circuit diagram embodying my invention,

Fig. 2 is a graphic representation of the operating characteristic of the tube shown in Fig. 1. ;j'

Referring to the accompanying drawing, there is shown an amplifier tube circuit in Fig. 1, the circuit showing only the connections to and from the amplifier tube for the sake'of simplicity. The input circuit A is coupled,as shown, to the grid-filament circuit of the tube A. T., the tube being any conventional transmitter amplifier tube, the plate, or output, circuit of which is energized by as' source of current B. The: grid of the tube is biased by a source of current C',-an'd includes, in circuit with the biasing source, a condenser C shunted by a resistance or leak R. I f

The input circuit A is coupled to the grid circuit of the tube at two points D', E, the

coupling E being effected between the condenser C and the grid of the tube, while the. coupling D is made to. a rectifier circuit shunted across the resistance R. The secondary coil of the coupling D has associated V therewitha variable slider 3 at one end thereof, and is connected at the other endfto any conventional rectifier device.

' The output from the slider 3 and rectifier is passed through a filtering section, the latter comprising choke coilsL L each of which coils is in series withthe slider 3 and the rectifier respectively, a condenser 0 be- -ing connected across the coil, the purpose of the filtering section being to smooth out'the pulsating direct current derived from the rec'- tifier.

' The operation of the circuit will appear obvious from the arrangement shown, 'it being understood that by properly proportioning thecouplings D, E, the leak resistance R, and the" condensers C C the amplifier grid can be kept just more negative than the value of the radio frequency input at Awhen large inputs occur, but very much negative when V in accordance with the change of input to the tube.

For example, in Fig. 2, I have shown what would happen on the characteristic curve of the tube A. T. when the input at A increases from one value to another, it being observed that when the increase occurs the operating point of the grid is moved from point 1 to point 2 on the characteristic curve, thus increasing the plate current flowing through the plate circuit of the tube only when the radio frequency inputincreases. 7

The grid of the tube A. T. is normallybiased highly negative by the source (1. The rectifier circuit is so arranged across the resistance R, that, when a radio frequency current flows cuit of the tube, said second source being of sufiicient magnitude to reduce the current flowing in the said anode circuit to substan tially zero in the absence of signal voltage in the said grid circuit, and a third source of potential disposed in said grid circuit, said third source being derived from said signal voltage source and arranged in opposition to said second source in such a manner that the operating grid potential of the tube is of suitable value for efficient amplification only while signalvoltage is impressed on the grid circuit of said tube.

WALTER VAN B. ROBERTS.

through the input A, a portion of the input is imposed upon the rectifier circuit through the coupling D while the remainder of the inputis imposed directly upon the coupling E. The slider 3 being positioned'for optimum operation, the rectifier will pass a puleating direct current through the filtersection, thepulsating current being smoothed be seen that I have eviseda methodand means for controlling. the consumption of plate current in an amplifier tube, used either in a transmitting or even in a receiving circuit. It is to be observed that this method not only conserves power, but also avoids the necessity for-running theplate of the tube at high temperatures during periods when signals are not being applied to its grid. Thus, the tube "may be arranged to utilize momentary over-loading during instants of great signal input without overheating the plate. v I

While I have indicated and described only one system for carrying my invention into efieet, itqwill' be apparent to one skilled in w i the art that my invention is by no means limited tothe particular organization shown and described, but that many modifications T in thecircuit arran ement as well as in the apparatus employe may be made without departing from the scope of my invention as set forth in the appended claim.

What I claim is:

An arrangement forreducing current losses in the anode circuitof a power amplifieritube comprising a source of signal voltage, a source of negative potential disposed in the grid cirlOll ice ice 

